Little is known about the extent of HIV infection among adolescents and young adults, or about the network and behavioral patterns in which they are engaged, or about the extent to which they are trying to reduce their risks. We also know little about how youth come to engage in high risk behaviors or to enter into sexual (or drug) relationships with persons who are more likely to be infected. There is an urgent need to learn the answers to these questions in order both to predict the future of the HIV epidemic and to be able to develop effective interventions against its spread among the young. We propose to answer these questions for a critical section of American youth -- those aged 18-21 who live in a neighborhood in which there are thousands of seropositive drug injectors. This will let us assess the extent to which HIV has spread to non- injecting heterosexual youth; the extent to which these youth have adjusted their behaviors to reduce their risk; and the extent to which their networks include drug injectors. The specific aims of this project are to determine, for the youth in this neighborhood: (l) HIV prevalence; (2) the prevalence of hepatitis B, hepatitis C, syphilis, and herpes simplex virus type 2, which are markers of high-risk behaviors; (3) the extent of high risk behaviors and of deliberate AIDS risk reduction; (4) behavioral and social risk factors for infection with HIV and the other agents; (5) how past peer relationships, family relationships, and relationships to social institutions such as school and religion affect later risk behaviors. After a pilot test, the study will interview a representative sample of 1200 of the 7 thousand youth in Bushwick. Sampling will involve two tiers: (l) for those with telephones, random dialing of telephones in the area to screen for and schedule interviews with a random sample of youth; (2) multiplicity sampling wherein the first tier youth will nominate a sample of youth without telephones. (Targeted sampling of high risk populations like crack smokers and the homeless will also be used if the first two tiers fail to recruit adequate numbers of these youth.) Bloods will be taken to test for infection, and interviews will determine present and past risk behaviors, present and past relationships to peers, family, and social institutions, and such individual level characteristics as sexual abuse, trauma, age of first sex, and non-injected drug use. Estimates will be made of the prevalences of infectious agents and risk behaviors. Statistical analysis will determine how present and past social and behavioral patterns affect the probability of infection with various agents; and how past social relationships affect current risk behaviors.